Throughout this description and the following claims, the bicycle derailleur that is referred to is the front derailleur. Such a derailleur is used to move the chain between the different toothed crowns (or toothed wheels) that form the so-called crankset of the bicycle. Typically, in racing bicycles the crankset comprises two or three toothed crowns.
The movement of the chain generally takes place by effect of the movement of a suitable thrusting member, commonly called cage fork or more simply cage. Such a cage is associated with an actuation kinematic mechanism that, deforming upon command by the cyclist, moves the chain from one toothed crown to another. The actuation kinematic mechanism is in turn associated with a derailleur body configured to be fixed to the frame of the bicycle, typically to the so-called seat tube of the frame (i.e. the tube arranged under the saddle).
The most common bicycle derailleurs are manually actuated. Recently, however, motor actuated derailleurs are on the market. In the latter the movement of the cage takes place by means of a motor member that is suitably driven, typically electrically.
The derailleur body is typically mounted on a support element projecting from the seat tube (typically welded thereon). Such a projecting element defines a shaped seat on which a corresponding coupling portion of the derailleur body is fixed in position (typically through a locking screw).
For the derailleur to operate correctly, it is necessary to position it precisely with respect to the crankset. In particular, it is necessary for the derailleur, in a rest configuration (i.e. in a condition in which the actuation kinematic mechanism is in the undeformed state), to have a desired relative position with respect to a reference toothed crown of the crankset that, typically, is the toothed crown with the largest diameter (hereafter: largest toothed crown). More specifically, it is necessary for the cage of the derailleur, in rest configuration, to be located at a desired distance from the largest toothed crown and with the respective middle plane as parallel as possible to the middle plane of the largest toothed crown.
In the prior art, the operator, after having mounted the crankset on the frame of the bicycle, manually positions the derailleur by eyesight with respect to the largest toothed crown of the crankset and fixes the derailleur in position on the projecting element by tightening the locking screw.
The Applicant has found that such mounting operations are particularly demanding, both in terms of time and in terms of the attention that the operator must pay. Moreover, the operator must be adequately trained in the mounting operations, so as to obtain a certain experience and familiarity with the task.